Question:
This question has Statement-1 and Statement-2. Of the four choices given after the Statements, choose the one that best describes the two Statements.
Statement-1: Short wave transmission is achieved due to the total internal reflection of the e-m wave from an appropriate height in the ionosphere.
Statement-2: Refractive index of a plasma is independent of the frequency of e-m waves.
This question has Statement-1 and Statement-2. Of the four choices given after the Statements, choose the one that best describes the two Statements.
Statement-1: Short wave transmission is achieved due to the total internal reflection of the e-m wave from an appropriate height in the ionosphere.
Statement-2: Refractive index of a plasma is independent of the frequency of e-m waves.
Statement-1: Short wave transmission is achieved due to the total internal reflection of the e-m wave from an appropriate height in the ionosphere.
Statement-2: Refractive index of a plasma is independent of the frequency of e-m waves.
Show Hint
Recall the refractive index of the ionospheric plasma: \(n = \sqrt{1 - \frac{81 N}{\nu^2}}\).
Updated On: Oct 31, 2026
- Statement-1 is true, Statement- 2 is false.
- Statement-1 is false, Statement- 2 is true.
- Statement-1 is true, Statement- 2 is true but Statement -2 is not the correct explanation of statement-1.
- Statement-1 is true, Statement-2 is true and Statement -2 is the correct explanation of Statement-1.
Show Solution
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The Correct Option is A
Solution and Explanation
Statement-1: Short waves (3-30 MHz) travel as sky waves; as they enter the ionosphere the refractive index decreases with height (electron density increases), so the ray bends away from the normal and is totally internally reflected back. This is true.
Statement-2: For a plasma, \(n = \sqrt{1 - \frac{81N}{\nu^2}}\) (\(N\) in \(\mathrm{m^{-3}}\), \(\nu\) in Hz), which clearly depends on the frequency \(\nu\). So Statement-2 is false.
Hence Statement-1 is true and Statement-2 is false.
Answer: (1) Statement-1 is true, Statement- 2 is false.
Statement-2: For a plasma, \(n = \sqrt{1 - \frac{81N}{\nu^2}}\) (\(N\) in \(\mathrm{m^{-3}}\), \(\nu\) in Hz), which clearly depends on the frequency \(\nu\). So Statement-2 is false.
Hence Statement-1 is true and Statement-2 is false.
Answer: (1) Statement-1 is true, Statement- 2 is false.
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